Search

Knee joint forces measured from instrumented implants provide important information for testing the validity of computational models that predict knee joint forces. The purpose of this study was to validate a parametric numerical model for predicting knee joint contact forces against measurements from four subjects with instrumented TKRs during the stance phase of gait. Model sensitivity to abnormal gait patterns was also investigated. The results demonstrated good agreement for three subjects with relatively normal gait patterns, where the difference between the mean measured and calculated forces ranged from 0.05 to 0.45 body weights, and the envelopes of measured and calculated forces (from three walking trials) overlapped. The fourth subject, who had a "quadriceps avoidance" external moment pattern, initially had little overlap between the measured and calculated force envelopes. When additional constraints were added, tailored to the subject's gait pattern, the model predictions improved to complete force envelope overlap. Coefficient of multiple determination analysis indicated that the shape of the measured and calculated force waveforms were similar for all subjects (adjusted coefficient of multiple correlation values between 0.88 and 0.92). The parametric model was accurate in predicting both the magnitude and waveform of the contact force, and the accuracy of model predictions was affected by deviations from normal gait patterns. Equally important, the envelope of forces generated by the range of solutions substantially overlapped with the corresponding measured envelope from multiple gait trials for a given subject, suggesting that the variable strategic processes of in vivo force generation are covered by the solution range of this parametric model., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

We examined the relationship between activity, peak load, medial to lateral load distribution, and flexion angle at peak load for activities of daily living. An instrumented knee prosthesis was used to measure knee joint force simultaneously with motion capture during walking, chair sit to stand and stand to sit, stair ascending and descending, squatting from a standing position, and golf swings. The maximum total compressive load at the knee was highest during stair ascending and descending and lowest during rising from a chair. Maximum total compressive load occurred at substantially different flexion angles ranging from 8.5 degrees during walking to 91.8 degrees during squatting. For all activities, total compressive load exceeded 2 times body weight, and for most activities 2.5 times body weight. Most activities placed a greater load on the medial compartment than the lateral compartment. Activities were grouped into three categories: high cycle loading (walk), high load (stair ascent, descent, and golf), and high flexion angle (chair sit to stand/stand to sit, and squat). The results demonstrate that the forces and motion sustained by the knee are highly activity-dependent and that the unique loading characteristics for specific activities should be considered for the design of functional and robust total knee replacements, as well as for rehabilitation programs for patients with knee osteoarthritis or following total knee arthroplasty., ((c) 2008 Orthopaedic Research Society)

This article begins to address the validation requirements of wear testing on total knee replacements in a knee simulator. The knee simulator has four stations. The axial force is variable but reaches a maximum of 2.3 kN. Physiologic anteroposterior shear force and rotational torques are supplied to the knee. The forces and displacements are timed to coincide with those of a typical gait cycle. Kinematics of the simulator are dependent on the type of knee being tested. Tests of designs with well known clinical histories were done to 10 million cycles. The relative amounts and types of wear shown by the designs were similar to that found in their clinical histories. Wear tracks on more conforming designs were larger, and the penetration into the plastic appeared to be less. This did not necessarily mean that wear, as measured by loss of material, was reduced on conforming designs. Delamination of the plastic was achieved only after aging the tibial components. Wear particles isolated from the lubricating fluid were similar in size and shape to those isolated from in vivo specimens. However, the relative amounts of wear particle shapes were different depending on the design. At the start of the tests, all of the flexibly mounted tibial components showed more motion than after 5 million cycles, indicating that the surface of the plastic became more conforming. This study showed that knee wear similar to wear observed in vivo can be reproduced in the laboratory. The parameters and methods elucidated in this introductory study should form the basis for use in preclinical wear tests of total knee replacements.

Wear of the polyethylene tibial components is a potential cause of failure in total knee arthroplasty. In addition to pitting, burnishing, and scratching, subtle striations on the bearing portion of the tibial surface have been observed in components retrieved relatively early after implantation. The striated pattern most typically occurred in areas centrally located within the articulating surface. The striations were anteroposterior directed and were identified as local cold flow at the surface. There was a strong correlation between the medial and lateral striated areas, suggesting that these patterns are related to cyclic rolling of the knee. The general characteristics and alignment of the striations could be attributed to the compressive and tractive forces occurring during femoral rollback. For the clinician, these results suggest that kinematics, as well as contact stress, should be considered when evaluating wear of polyethylene components.

The functional influence of patellofemoral design was evaluated by testing two cohorts of patients with total knee arthroplasty while walking, climbing stairs, and rising from a chair. The two cohorts received one of two different designs of total knee arthroplasty. The designs differed primarily in the curvature of the femoral trochlea. These differences in curvature have been shown in in vitro studies to influence the tracking of the patella. One design had a smaller radius on the patellar flange, which caused the patella to articulate more anteriorly and distally than the second design, which had a larger radius in this region. The second design more closely replicated the curvature of the femoral trochlear anatomy. There was a significant functional difference during stairclimbing between the patient groups, whereas there was no difference during walking or chair rising. The group with the design that had nonanatomic tracking of the patella had a higher than normal moment tending to flex the knee (net quadriceps moment) during late stance phase. The increased net quadriceps moment during late stance was concurrent with an increased knee flexion. The abnormal function occurred when the patellar was tracking over the nonanatomic portion of the trochlea. Patients in the group with the anatomic trochlea did not have abnormal function. These results suggest a relationship between a nonanatomic trochlea and abnormal function during stair-climbing.

Wear at the polyethylene tibial plateau in total knee arthroplasty (TKR) is one of the primary concerns with these devices. The artificial bearing of a TKR has to sustain large forces while allowing the mobility for normal motion, typically, rolling, gliding and rotation. The tractive forces during the rolling motion at the knee joint were analyzed to determine which factors cause these forces to increase in TKR. The implications of these tractive forces to polyethylene wear were considered. Traction forces were calculated using a model of the knee to evaluate the effect of variations in the coefficient of friction, gait characteristics, antagonistic muscle contraction and patellofemoral mechanics. The model was limited to the sagittal plane motion of the femur on the tibia. The input for the model was the shape of the articulating surface, coefficient of friction, contact path, muscle anatomy and gait kinetics common to patients with a total knee replacement. The generation of tractive forces on the tibial polyethylene plateau was highly dependent on the static and dynamic coefficient of friction between the femur and the tibia. A peak tractive force of approximately 0.4 body weight was calculated with a peak normal force of 3.3 body weight. Tractive rolling occurred during most of stance phase when the static coefficient was 0.2. Alterations in gait patterns had a substantial effect on the generation of tractive forces at the knee joint. When an abnormal gait pattern (often seen following TKR) was input to the model the posteriorly directed tractive force on the tibial surface was reduced. It was also found that variations in muscle contractions associated with antagonistic muscle activity as well as the angle of pull of the patellar tendon affected the magnitude of tractive forces. The results of the study suggest that there are feasible conditions following total knee replacement which can lead to tractive forces during rolling motion at the tibiofemoral articulation that should be considered in the analysis of factors leading to polyethylene damage in total knee replacement.

Gait analysis was used to study patients who underwent cemented medial unicompartmental knee arthroplasty (UKA) for medial compartment degenerative knee disease. All had excellent clinical function of the operated knee, with minimal involvement of other joints. Ten patients met the inclusion criteria for this study. Gait findings from this study group, as well as those from a similar cohort of patients who had undergone total knee arthroplasty (TKA), were compared with those for a group of normal patients. A greater percentage of patients (7 of 10) following UKA maintained the normal biphasic flexion/extension moment pattern about the knee or demonstrated a quadriceps overuse pattern, when compared with similar groups following TKA. In addition, the adduction moment in patients following UKA was significantly larger than in patients following TKA. The postoperative limb alignment correlated with the peak adduction moment recorded during the patient's gait analysis. The postoperative alignment may explain the differences in the adduction moment between the UKA and TKA patients, as there tended to be residual varus in the UKA population. The results of this study imply that preservation of the anterior cruciate ligament during UKA allows patients to maintain normal quadriceps mechanics, and that residual varus alignment subjects a medial UKA to higher loads.

This paper examines the biomechanics of total knee arthroplasty as a treatment for arthritis and anterior cruciate ligament (ACL) reconstruction for repair of torn anterior cruciate ligaments of the knee. These are two of the most frequent reconstructive procedures for the knee joint. Functional testing of patients while performing various activities of daily living was used to study the relationship between the intrinsic biomechanics of the knee and function. The results of the study of patients following total knee replacement demonstrated a dynamic interaction between the posterior cruciate ligament and quadriceps function during stairclimbing. The study of patients with ACL-deficient knees demonstrated that loss of the anterior cruciate ligament can cause the avoidance of quadriceps contraction during activities when the knee is near full extension. Other studies demonstrated a relationship between tibiofemoral joint mechanics and patellofemoral mechanics. In addition, the importance of combined ligamentous laxity with higher than normal adduction moments during gait was examined in relationship to progressive degenerative changes to the medial compartment of the knee. In summary, functional testing such as gait analysis has proven to be an important basic research tool as well as extremely effective for clinical testing of new procedures and devices.

Twenty-one knees in 14 patients were studied during walking, in clinical follow-up, and radiographically. The purpose was to examine the relationship between dynamic loading at the knee joint during level walking in the early postoperative period (1-2 years) and longer-term (4 years) prosthetic performance. Joint kinematics and kinetics were measured while patients were walking in the laboratory. The results were compared with an age-matched control group of healthy normal subjects. Patients were analyzed when grouped according to original diagnoses of rheumatoid or osteoarthritis. After total knee arthroplasty, patients with rheumatoid arthritis walked with a significantly lower magnitude peak adduction moment (force tending to thrust the knee into varus) about the knee than patients with osteoarthritis. The osteoarthritic group had an increased varus axial alignment when compared to the rheumatoid group. There was a strong correlation between postoperative varus alignment and the magnitude of the adduction moment. These results suggest that dynamic loading at the knee is greatly affected by static alignment of the joints in patients with total knee arthroplasty. In spite of the lower adduction moment during level walking and its associated effects on lower compressive loads at the knee, the patients with rheumatoid arthritis had a significantly higher radiolucency index. Thus, it appears that quality of bone stock may be a more important factor in determining prosthetic loosening than dynamic loading at the knee joint following total knee arthroplasty.

Retention of the posterior cruciate ligament in total knee arthroplasty is discussed in biomechanical and clinical terms and the implications for design, kinematics, function, and prosthesis longevity considered. The specific roles of passive range of motion, femoral rollback, stresses on the implant-bone-prosthesis cement system, and wear are examined. The authors argue that the posterior cruciate ligament improves passive range of motion, the mechanical efficiency of the knee musculature and thus improved stairclimbing efficiency, reduces stress at the cement-bone-implant interfaces, and has little or no impact on the polyethylene wear problems.

The authors quantitatively evaluated the relationship between component placement, limb alignment, and function following unicompartmental knee replacement surgery. It was found that anatomic alignment, prosthetic positioning, and prosthetic design influence the patients' ability to walk and climb stairs. There was wide variation in the placement of the tibial and femoral component among patients. The placement of the femoral component corresponded directly to function during stairclimbing and level walking. Anterior malpositioning of the femoral component resulted in reduced ability to climb stairs. The tibial component position varied primarily in varus-valgus position. Varus-valgus alignment in the frontal plane correlated directly with the magnitude of the adduction moment during level walking. A varus alignment produced a twofold increase in the magnitude of the adduction moment at the knee during walking. Given the potential advantages of the unicompartmental knee, improved precision in component placement should improve the long-term results of hemiarthroplasty knee surgery.

One hundred twenty-two total knee arthroplasties were performed with porous ingrowth fixation of the patellar component between February 1984 and February 1987. Twelve subsequently have experienced fatigue fracture of the patellar component at the peg-plate junction. All fractured patellar components demonstrated excellent ingrowth and fixation of the porous titanium fiber mesh-peg surfaces with no ingrowth into the porous plate underlying the polyethylene patellar surface. While the initial group of 122 arthroplasties was only slightly greater than one-third male, the preponderance of patellar fractures was in males (ten of 12). Patients with patellar component failure were on average younger and heavier and had a greater range of knee motion than the index group. The average time from implantation to recognition of fracture was 24 months. Biomechanical analysis of the force system about a domed patella demonstrated that loading of the patellofemoral joint results in eccentric loading of the dome surface. Peg fixation not accompanied by fixation of the overlying plate allows these high eccentric forces to load the peg-plate junction in shear with consequent fatigue at the peg-plate junction. These results indicate that the shear forces are sufficiently high to warrant caution in the use of peg-plate systems in which peg ingrowth without plate ingrowth occurs.(ABSTRACT TRUNCATED AT 250 WORDS)

The biomechanics of the knee joint provide an important basis for the rationale in the design and selection of appropriate total knee arthroplasty. This article examines knee biomechanics in terms of patient function, prosthesis design, cruciate ligament retention, alignment, and fixation of the tibial component. While design and surgical technique for total knee replacement progress, a better understanding of the characteristics of joint loading, stress distribution, and the biologic response of bone to stress will provide the potential to improve both function and implant longevity.

Twenty-six knee arthroplastics in 22 subjects were studied clinically and in a gait laboratory before and on one or more occasions after surgery. The purpose was to identify changes in gait characteristics and relate them to changes in the clinical situation of the patients. The gait patterns of the patients changed following surgery mainly with respect to their time-distance characteristics; stride length, cadence, time of swing, and time of support. Positive correlations were noted between these gait changes and the patient's pain, his limp, and his walking distance. It is concluded that the information obtained in sophisticated gait laboratory is of limited value to the surgeon in his clinical assessment.

A primary goal of total knee replacement has been the relief of pain. As new implant designs evolve and other improvements take place, we must broaden our goals to include increased longevity and an improvement in patient function, especially among younger patients. There is a relationship between the longevity of the implant and patient function, since function determines loads on the joint and the motion of the joint. In addition, ultimate breakdown of the prosthesis depends upon these same loads. This paper will first discuss the relationship between function and some of the intrinsic mechanics of the knee joint, and then the relationship between function and mechanics and the longevity of the implant. It is based on an analysis of patients with a variety of differently designed total knee replacements that replicate, to a greater or lesser degree, the anatomy of the knee joint. Some of the implants sacrifice both anterior and posterior cruciates, and some retain both.